1. Field of the Invention
The present invention relates generally to vacuum holddown apparatus and methods of operation and, more specifically, to a cut-sheet print media vacuum holddown particularly useful for a hard copy apparatus, such as an ink-jet printer.
2. Description of Related Art
It is known to use a vacuum induced force to adhere a sheet of flexible material to a surface, for example, for holding a sheet of print media temporarily to a platen. [Hereinafter, xe2x80x9cvacuum induced forcexe2x80x9d is also referred to as xe2x80x9cvacuum induced flow,xe2x80x9d xe2x80x9cvacuum flow,xe2x80x9d or more simply as just xe2x80x9cvacuumxe2x80x9d or xe2x80x9csuctionxe2x80x9d.] Such vacuum holddown systems are a relatively common, economical technology to implement commercially and can improve machine throughput specifications. For example, it is known to provide a rotating drum with holes through the surface so that a vacuum through the drum cylinder provides a suction force at the holes in the drum surface. [The term xe2x80x9cdrumxe2x80x9d as used hereinafter is intended to be synonymous with any curvilinear implementation incorporating the present invention; while the term xe2x80x9cplatenxe2x80x9d can be defined as a flat holding surface, in hard copy technology it is also used for curvilinear surfaces, such as a common typewriter rubber roller; thus, for the purposes of the present application, xe2x80x9cplatenxe2x80x9d is used generically for any shape holddown surface used in a flexible material holddown apparatus.]
Generally in a hard copy apparatus implementation, the platen is used either to transport cut-sheet print media to a printing station of a hard copy apparatus, such as a copier or a computer printer, or to hold the cut sheet print media at the printing station while images are formed (also known as the xe2x80x9cprint zonexe2x80x9d), or both. [In order to simplify discussion, the term xe2x80x9cpaperxe2x80x9d is used hereinafter to refer to all types of print media. No limitation on the scope of the invention is intended nor should any be implied.]
One universal problem, particularly pertinent in the adaptation of a vacuum holddown to use in a hard copy apparatus, is the management of different sizes, shapes, and thicknesses of available paper. Open holes around the edges of a sheet smaller than the dimensions of the vacuum field across the platen surface results in vacuum losses and a lower or ineffective holding force. In other words, too many exposed vacuum ports result in a loss of suction at the platen surface and the paper is not firmly adhered to the surface.
One technique for controlling a vacuum holddown is proposed by Rasmussen et al. in U.S. patent application Ser. No. 09/292,767 for a PRINT MEDIA VACUUM HOLDDOWN (assigned to the common assignee of the present invention and incorporated herein by reference). A vacuum holddown for sheet materials has a surface having a field of vacuum ports in which each individual port is gated. When a vacuum is applied to the underside of the holddown, the gates close. When a sheet of material is introduced onto a region of the field, the gates only within vacuum manifold passageway covered by the material are configured to spring open, applying a suction force to the sheet via the now opened ports. The holddown thus automatically adjusts to material size. An implementation for use in an ink-jet printer with cut-sheet print media is demonstrated.
Another technique is demonstrated by Rhodes et al. in U.S. patent application Ser. No. 09/292,125 for a VACUUM CONTROL FOR VACUUM HOLDDOWN (assigned to the common assignee of the present invention and incorporated herein by reference). A mechanism for manifolding a vacuum force to separate surface sectors of a vacuum holddown uses subsurface ducting to apply the vacuum to separate subsurface vacuum plenums wherein each is fluidically coupled to a separate surface sectors. The plenum is segregated by a diaphragm into surface side and vacuum side cavities. Trigger ports and appropriate ducting through the holddown subjacent the surface associated with each sector determine how the vacuum is routed. Only when a trigger port is covered is the vacuum routed to the surface sector associated therewith. The system can be implemented in planar or curvilinear constructs and be provided with features to accommodate a near-continuous range of flexible material sizes. A specific implementation in an ink-jet hard copy apparatus is also described.
Related to the Rasmussen et al. and Rhodes et al. Applications, U.S. patent application Ser. No. 09/292,838 for a VACUUM SURFACE FOR WET DYE HARD COPY APPARATUS by Wotton et al. (assigned to the common assignee of the present invention and incorporated herein by reference) shows a platen surface structure construct, particularly useful in a hard copy apparatus for a vacuum holddown, configured by dimensioning print media platen surface structure channels and ports in order to ensure print media leading edge and trailing edge holddown. The vacuum is distributed across the platen surface in accordance with predetermined dye flow characteristics based upon known dye composition and known print medium composition and such that print artifacts are not created by vacuum pulling wet dye through the capillaries of the medium.
There is a continuing need to direct vacuum forces to specific locations of a holddown to increase vacuum efficiency and improve holddown force. Moreover, there is a need for a vacuum holddown for sheet material transport that can adjust to hold a variety of sizes of materials.
In its basic aspects, the present invention provides a vacuum holddown apparatus, having a vacuum source, including: at least two sheets of material, said sheets separating a substrate held by vacuum from the vacuum source, wherein each of the sheets is provided with a plurality of vacuum ports and each sheet has a different pattern of the vacuum ports; and said sheets are mounted in sliding contact engagement such that shifting said engagement varies the pattern of vacuum application through the pair.
In another aspect, the present invention provides a method for distributing a vacuum holddown vacuum force to a substrate holding surface having a plurality of vacuum transmitting first apertures therethrough in a first predetermined pattern, the method including: adjacently to said surface, mounting a valve for redistributing the vacuum force between predetermined sets of channels wherein said valve has a complementary shape and size with respect to said surface, said valve means having vacuum transmitting second apertures therethrough arrayed in a second predetermined pattern; and selectively moving the valve to align selected ones of said second apertures to selected ones of said first apertures in accordance with producing a predetermined vacuum force distribution at said first surface.
In yet another aspect, the present invention provides a hard copy apparatus, having a vacuum source producing a predetermined vacuum force, the apparatus including: a platen having a holddown surface and a plurality of vacuum transmitting first apertures therethrough channels in a first predetermined array, each of the first apertures fluidically coupling the vacuum force to the surface; and mounted in sliding abutment and separating the platen from the vacuum source, at least one vacuum distribution altering device having vacuum transmitting second apertures therethrough in a second predetermined array such that discrete positions of the vacuum distribution altering device with respect to the platen produce discrete vacuum force patterns at the surface.
In another aspect, the present invention provides a vacuum drum printer vacuum drum device including: a drum having a plurality of vacuum channels in a first predetermined array across a drum outer surface, each of the vacuum channels having a vacuum port fluidically coupling an associated vacuum channel to a drum inner surface; and mounted within the drum, at least one sleeve having a sleeve outer surface in sliding face-to-face contact with the drum inner surface and having apertures therethrough in a second predetermined array such that discrete sleeve positions produce discrete vacuum patterns at the outer surface of the drum.
Some of the advantage of the present invention are:
it provides a means for directing vacuum forces to specific areas for maximum media hold down;
it provides improved vacuum efficiency by making an adjustment as a variable sized sheet is delivered to the holddown, focusing the highest vacuum forces at the leading edge and a region where the rest of the sheet progressively comes into contact with the holddown;
it supplies the highest relative vacuum forces on the leading and trailing edges of the sheet;
it is useful to adjust for different widths of sheets by sealing off the vacuum ports with are outside a chosen sheet width;
it provides a low cost manufacturing solution to the problem of distributing vacuum forces across a holddown where adjustment for held sheet widths is required; and
in a vacuum drum hard copy apparatus implementation, a paper transport system implementation is operable while being moved at a relatively high speed of rotation.
The foregoing summary and list of advantages is not intended by the inventor to be an inclusive list of all the aspects, objects, advantages and features of the present invention nor should any limitation on the scope of the invention be implied therefrom. This Summary is provided in accordance with the mandate of 37 C.F.R. 1.73 and M.P.E.P. 608.01(d) merely to apprise the public, and more especially those interested in the particular art to which the invention relates, of the nature of the invention in order to be of assistance in aiding ready understanding of the patent in future searches. Other objects, features and advantages of the present invention will become apparent upon consideration of the following explanation and the accompanying drawings, in which like reference designations represent like features throughout the drawings.